I guess the question becomes then why did putin start the war without sufficient buildup of missile reserves to flatten Kyiv in the first few days? And why not contract with israeli defense companies for precision missile technology? It doesn't seem like their relations are really that severed even with the whole Iran issue. One would also think China might also appreciate a client willing to battle test their precision military hardware.

You'll have to ask Putin that question. But the usual intelligence analysis of that decision is based on several factors.

1. Putin thinks the disintegration of the USSR in 1991 was a historic disaster and wants to reassemble much of it as some sort of new "Russian Empire" in order to control more resources and establish defensive space to protect the motherland against a future foreign invasion. He sees Ukraine as a fake country.

2. Russian demographics are collapsing and Putin himself is aging so this was his last chance to take decisive action. Despite limited stockpiles of advanced weapons, waiting would have made an invasion even harder.

3. Putin has surrounded himself with loyal yes-men who curried favor by telling him what he wanted to hear instead of giving him accurate information about Ukrainian politics and military capabilities.

4. Putin perceived Joe Biden as being particularly weak and unlikely to take decisive action.

5. Russia's recent invasions of Georgia (2008) and Ukraine (2014) had gone fairly well so it wasn't irrational to expect a rapid victory.

To be clear I'm not trying to justify or excuse Putin's decision (I hope he loses) but rather to explain how he might have reached it.

Israel isn't going to sell advanced weapons to Russia in current circumstances. It would be impossible to hide. Intelligence analysts can pick apart little fragments from a missile explosion and determine where the components were made. It's not technology that Russia lacks but the capacity to manufacture that technology at scale with acceptable quality.

China is making a fortune selling weapons and dual-use equipment to both Russia and Ukraine. But they don't sell the good stuff because they don't want sensitive technology to fall into US hands, and because they want the option to bite off a chunk of Russian territory later.

Because "Flatten a city" actually takes dramatically more scale than anyone has seen in decades.

40k Tons of bomb were dropped on Berlin in WW2. That's nearly all explosive payload too.

That's about equivalent to 80k modern cruise missile warheads.

The US has built less than 5000 Tomahawk missiles ever.

Russia has fired approximately 6000 missiles into Ukraine in the course of the war.

This is why the US still maintains a fleet of ancient "Bomb Truck" style bombers in the B52. Nothing compares to 100 B52s flying over a target for weeks. They allowed us to drop 20k tons of bombs on Vietnam and the surrounding countries. A horrific capability.

Gaza is a combination of Israel being utterly fucking insane and apparently desiring to terrorize people, and the fact that Gaza is super tiny.